An air bag system for restraining a vehicle occupant commonly includes an inflator containing gas generating material which, when ignited, rapidly produces a large volume of gas for inflating the air bag. Such a system also includes a collision sensor. The collision sensor senses the occurrence of a predetermined amount of vehicle deceleration indicative of a collision, and completes a circuit to provide an electrical signal upon sensing such vehicle deceleration. The gas generating material in the inflator is ignited in response to the electrical signal. The gas generating material is thus ignited to produce the gas for inflating the air bag upon the occurrence of a vehicle collision.
The inflator may become subjected to abnormally high ambient temperatures if, for example, the vehicle is involved in a fire. The gas generating material could then become heated to a temperature at which it is ignited by the heat of the fire. It is known to include an auto-ignition material in the inflator to prevent the gas generating material from being ignited at a time when the ambient temperature of the vehicle has reached an excessively high level. The auto-ignition material will ignite at a temperature that is lower than the temperature at which the gas generating material will ignite. When the ambient temperature of the vehicle reaches the ignition temperature of the auto-ignition material, the auto-ignition material ignites automatically. The auto-ignition material then produces products of combustion that ignite the gas generating material. The gas generating material is thus ignited before the ambient temperature of the vehicle reaches an excessively high level.